(1) Field of the Invention
The present invention relates to switching amplifiers and particularly to such amplifiers for use in the generation of audible warning signals. More specifically, the present invention is directed to a reduction in the size and cost of means for amplifying signals having a rectangular wave form and especially to the provision of a compact electronic siren having high reliability. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well-suited for use in the generation of audible warning signals. Electronic sirens are, of course, well-known in the art. The typical prior art electronic siren, for example the apparatus disclosed in my U.S. Pat. No. 4,363,028 issued Dec. 7, 1982, is a comparatively sophisticated device capable of multi-mode operation. Thus, the electronic siren may selectively be operated as a audible warning signal generator, a public address system or a radio repeat device. Further, in the warning signal generation mode the prior art devices could typically be caused to selectively produce sounds having differing characteristics such as, for example, a "wail", a "yelp", a multiple tone or an air horn simulation. This multi-mode capability has necessarily required that a user having less demanding requirements pay penalties from the viewpoint of equipment cost and size.
There has been a long-standing demand for an electronic siren characterized by moderate cost and comparatively small size, so as to facilitate installation in so-called compact vehicles, which was at least comparable to the prior art devices in reliability and power handling capability. This long-standing demand has not been met at least in part because of the unavailability of a suitable circuit for amplifying the rectangular waveform audio frequency signals which will cause production of the desired sound when applied to a loud-speaker. Specifically, prior art power amplifiers of comparatively small size and moderate cost were not capable of reliably operating in a switching mode in response to a retangular waveform provided by oscillator means which may be controllable.